This invention relates to radiometric apparatus and more particularly to such apparatus which employs a periodically energized, light-emitting diode to obtain a null balance relative to chopped radiation received from a target.
Various types of radiometric apparatus are known in the art for the non-contact measurement of temperatures. The object whose temperature is being measured is generally referred to as the target. One of the most accurate types of radiometric apparatus is that which operates in a null balance mode. In this mode of operation, the target radiation is compared with the radiation obtained from a reference source, typically, an incandescent lamp. The radiation components from the target and the reference source are chopped out-of-phase before being applied to a common detector and the output signal from the detector controls a servo loop which energizes the reference lamp in a sense tending to minimize the difference between the two energy levels. The level of energization of the reference source is then indicative of the target temperature. While this type of system attains a relatively high degree of accuracy, since the characteristics of the reference lamp are typically much more predictable and accurately known than those of commonly used detector elements, the reference lamps do gradually decay in emissivity and ultimately burn out.
Among the several objects of the present invention may be noted the provision of radiometric apparatus which will determine the temperature of target objects with high accuracy and stability; the provision of such apparatus which will operate for long periods without recalibration; the provision of such apparatus which is highly reliable and which is of relatively simple and inexpensive construction. Other objects and features will be in part apparent and in part pointed out hereinafter.